(1) Field of the Invention
The present invention relates to the field of fluid drainage installations that are fitted to motor-driven aircraft, in particular rotorcraft, in order to evacuate the liquid that is contained in a compartment housing an engine of the aircraft.
(2) Description of Related Art
Engined aircraft, such as airplanes or rotorcraft, for example, have a power plant including one or more fuel-burning engines to provide the aircraft at least with propulsion. The engine(s) is/are installed on board the aircraft in compartments that are reserved for engines, which engines may for example be of a combustion engine type or of a turboshaft engine type, and make use of a liquid fuel.
There arises the problem of making the aircraft safe relative to flammable liquid(s) stagnating inside one or each compartments respectively housing an engine, commonly referred to as “engine compartments”. Flammable liquid(s) stagnating in one or more engine compartments is a potential source of danger because of the high temperatures that exist in the environment close to the power plant. Such flammable liquids are constituted in particular by fuel and/or lubricant that has accidentally escaped from the power plant, or indeed by a residue of liquid used during maintenance of the power plant, for example.
That is why aircraft are fitted with an installation for draining the liquid that might potentially stagnate inside one or more engine compartments in order to collect said liquid and discharge it to the outside of the aircraft. The liquid that needs to be drained comprises not only flammable liquid(s), but also water that may potentially have infiltrated into the engine compartment(s), and potentially in large quantities.
Such drainage installations comprise a drainage line in fluid flow communication with a liquid collector provided in the bottom of a given engine compartment. The liquid that might stagnate in the engine compartment is drained via the collector, which collector includes at least one opening placed in communication with an upstream inlet of the drainage line. The liquid evacuated from the collector through the opening is conveyed via the drainage line in order to be discharged to the outside of the aircraft via a downstream outlet of the drainage line.
In this context, there arises the problem of organizing the drainage installation while taking various constraints into account.
One constraint relating to the organization of the drainage installation lies in the potential low pressure state inside the engine compartment relative to the surrounding pressure outside the rotorcraft. An engine compartment in a low pressure state may be due in particular both to air flowing inside the drainage line and also to openings in the engine compartment leading to the outside of the aircraft.
The low pressure state of the engine compartment also increases with increasing altitude and/or forward speed of the aircraft, or indeed, in the specific circumstance of a rotorcraft, depending on the orientation of the blast of air produced by a main rotor having a substantially vertical axis that is installed above and close to the power plant in order to provide the rotorcraft at least with lift.
Still in the circumstance of a rotorcraft, the drainage line is typically installed going from the top of the rotorcraft towards its bottom, thereby leading to a pressure difference between the upstream inlet and the downstream outlet of the drainage line. For some other type of aircraft, having a longitudinal extent between the front and the rear that is considerable, such as for an airplane, the drainage line may extend so as to run along a low slope.
It is found that said low pressure state in the engine compartment constitutes an impediment against evacuating the liquid through the drainage line. Consequently, it is known to provide an obstacle in the drainage line between the collector and a downstream zone of the drainage line, which obstacle serves to retain the liquid drained by the collector. The liquid retained upstream from the obstacle is spontaneously discharged to the downstream zone of the drainage line as soon as the pressure of the column of retained liquid is sufficient to overcome the pressure difference between the collector and the downstream outlet of the drainage line.
By way of example, such an obstacle may be formed by a valve that can be caused to open at a given pressure threshold, such as described for example in Document EP 1 062 155 (Allied Signal Inc.), or also by way of example it may be formed by a constriction arranged in the drainage line, as described by Document EP 2 620 361 (Airbus Operations SL). Reference may also be made to Document U.S. Pat. No. 3,371,482 A.A.M.L. Camboulives et al.) and US 2006/249628 (Jeffrey Turner et al.), each of which describing a cell for an airplane turboprop, which cell has a drainage duct. According to U.S. Pat. No. 3,371,482, the drainage duct is fitted with a valve that is urged towards an open position and that closes in the event of excess pressure. According to US 2006/249628, the drainage duct is provided at its trailing edge with a deflector for guiding fluids away from the cell.
Another constraint relating to the organization of the drainage installation lies in making it safe relative to potential propagation of flames from the collector towards the drainage line in the event of a fire in the engine compartment(s). For this purpose, one or more ducts forming the drainage line are conventionally made using a fireproof material. It has been found that a drawback of such provisions lies in increasing the weight, the bulk, and/or the cost of obtaining the drainage line.
In this context, and given the continuing search in the field of aviation seeking to make rotorcraft safe against the propagation of a fire, if any, it is appropriate to improve the conditions for preserving the drainage installation by preventing flames from passing from the collector towards the drainage line.
In various fields, it is known to use firebreak grilles as obstacles to the passage of flames through an opening in the event of a fire. Such firebreak grilles are used conventionally in the field of construction, for example.
Nevertheless, the constraints due to said low pressure state of the engine compartment make it awkward to adapt such firebreak grilles to the field of aviation. It is, however, useful to seek a solution that enables the opening of the collector to be provided with such a firebreak grille.
Indeed, fitting the opening with a grille presents other advantages, such as that of retaining any solid bodies that might be present inside the collector so as to prevent them from passing into the drainage line. It is appropriate to avoid the drainage line becoming clogged by such solid bodies, not only to avoid constituting an obstacle to the flow of the liquid along the drainage line, but also they might potentially be flammable.
Nevertheless, although such firebreak grilles can present the advantage of retaining said solid bodies, they are conversely also likely to constitute an obstacle to passing not only the liquid through the opening of the collector, but also to passing air rising towards the collector on being expelled by the liquid flowing through the drainage line.
That is why it is common practice in the field of aircraft to keep clear the opening of the collector in order to enhance the freedom of the fluid drained by the collector to flow therethrough while avoiding excessively increasing the cross-section of the ducts forming the drainage line.
In the context of another constraint relating to organizing the drainage line, any such increase in the cross-section of the duct(s) is undesirable.
More particularly, the drainage line extends along or is incorporated in the walls of the aircraft. Consequently, it is desirable for the drainage line to be of size and weight that are as small as possible in order to make it easier to incorporate on board the aircraft.